Determine/document support for Apple Xcode 12

[Paul Hargrove]

We should determine if there are any problems with Apple Xcode 12 (now in Beta) and document the status.

[Paul Hargrove]

I have installed "Xcode 12 Beta 6" (Build version 12A8189n) on my laptop running macOS Catalina (10.15.5). I am able to pass make dev-check (for smp and udp).

This is a minimum requirement, and not (IMO) sufficient to document this compiler as supported until we have some coverage by periodic testing. Additionally, the beta process is not complete, and so any claim of support now is premature.

This Xcode does not run on older macOS, but will run on macOS 11 "Big Sur" (determining support for which is the subject of issue 410).

[Paul Hargrove]

Initial testing on macOS 11 with this beta compiler release is also positive.
More complete details appear in issue 410.

Some "history" is still needed to build confidence, as is a final (non-beta) release.

[Paul Hargrove]

Apple has released Xcode 12 (non Beta).
I will conduct retesting and work toward the necessary level of confidence to consider this a "supported" compiler.
However, since we do not document "ceilings" for compiler support, I don't believe a positive outcome to testign will require any documentation updates.

[Paul Hargrove]

As noted previously, Xcode 12 was released almost 2 months ago. It has been in our Catalina-based nightly testing for most of that time with no compiler-specific issues.

No documentation updates are required.

[Paul Hargrove]

Correcting status to Resolved